WIKA FLM Benutzerhandbuch

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WIKA operating instructions level sensor model FFG

7

13445627.01 12/2010 GB/D/F

The level sensor shown in figure 2 serves for the continuous

measurement of fluids. To transmit the liquid level value to the sensor, a

float is sliding on the sensor tube. The operating principle of the sensor

is based on the magnetostriction effect. The float contains a magnet

while a wire made of magnetostrictive material is installed under tension

inside the sensor tube. The magnetic field of the float is twisting the

wire. A second, temporary magnetic field is generated along the wire by

a current pulse within the wire. The superposition of the two magnetic

fields will release a mechanical wave on the wire.

At the end of the wire within the sensor head, the mechanical wave is

converted by a piezo-ceramic transducer into an electrical signal. The

starting point of the mechanical wave and, hence, the float position is

then determined by measuring the transit time.

The results of such measurements are feasibility-tested by a microcon-

troller located in the sensor head and are then converted into a current

value by a digital analog transformer. The sensor is provided with a

2-wire connection so that the current consumption indicates the position

of the float at the same time. The current values are restricted to a range

of between 3.5 ... 23 mA.

2. Description of functions and design

Fig. 1: Level sensor system model FFG

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